cveklund

I have an 85 GS that I just recently swapped a GSL rear end into. I didn't drive it hardly at all befor I did the swap, but now when I stop, the brake pedal is firm, but then slowly falls to the floor. If i take my foot off and put it back on, it gets firm, then slowly goes to the floor again. My dad thought it was the brake booster, and the guy at autozone thought it was the master cylinder. Has anyone had the same problem? In the swap, I just swapped the rear end, not the other parts. I was told I didn't need to swap them. If I should have please let me know.

Thanks,
Chris

specRX7_22

last season, my dad had a similar problem in that hed have to pump up the pedal to get any pressure. after replacing 3 master cylinders, rebuilding calipers, already had braided steel lines, gravity bleeding, ridding the car of the speed bleeders (which werent the problem, so dont stop using them if you have them), and some other things. the LAST thing we checked was the booster, and sure enuf that was the problem. this is strange becuz ud normally think that a bad booster would give a stiff pedal, but other ppl said they'd heard of it giving a soft pedal before.

if i was in your situation, id just replace the booster and master cylinder, it cant hurt.

Rx7r4c3r

I have a 82 gs and recently swapped in a gsl rear end. I have the exact same problem. Before the swap I had perfect brakes. After the swap my braking is like yours. I bled everything and checked for leaks. When getting someone to apply the brakes I found abit of air coming from in between the master cylinder and brake booster. For a quick temp fix I put some coldweld on. No more air coming from there now when the brakes are applied. We re-bled the brakes again still the same affect. When you pump the breaks I find the back brakes will lock up first. I heard drum brake balancers keep 5 psi in the rear lines for the rear wheel brake cylinders. This may be why we do not have proper braking. I think I am going to the junk yard tommorow and picking up a gsl brake balancer. The only other thing I have not done is bled my master cylinder because it did go dry. My breaks will eventually stop me but not fast. When the car is of the brakes feel great. When the car is on the brakes go to the floor. There has been no loss of fluid in my master cyclinder. I will try the new brake balancer and let you know.

MarkPerez

I swaped rearends on my 82 GS from drum to disk and have had NO problems at all.

cveklund

Did you swap the master cylinder, brake booster, or brake balancer? I know there are two different master cylinders, but not sure about the rest.

JEC-31

Yeah, it's alot more work, but when swapping in bigger brakes it's important to also get the rest of the system. Brake systems are touchy and all components need to be balanced against each other.

I'd upgrade the whole system, including the fronts, to keep the front/rear balance.

Also, Summit Racing sells front/rear bias proportioning valves, that might be a way to go.

Just my .02

- Josh

MarkPerez

Nope, just the rearend, brake lines, and e-brake cable.

specRX7_22

yeah i was gonna say... that sounds like a bias problem to me.

cveklund

Aren't the front brakes on the GS the same as the GSL? I was thinking of the brake balancer also. Let me know what you find out.

cveklund

How much are the Summit Bias Proportinging valves, and what is the part number. Also, I know this may sound dumb, but where do you install the proporting valve thingy?

Thanks,
Chris

MarkPerez

i'm pretty sure it replaces the brake 'rail' where all the brake lines meet under the master cycl. yes the front brakes are the same on GS and GSL.

hornbm

I would like to hear the verdict on this. I'm going to swap a GSL rear end on my 85 GS as well.

FYI If anybody has a GSL rear end they'd like to sell PLEASE PM me

MarkPerez

UPDATE,, also i think 84 and 85 are different and of coarse the -SE's or call it series 3,, i guess 81 - 83 are pretty much the same.

cveklund

Does anyone know about the Summit part number or is it a better idea to get one from the boneyard from the from the same car I got the rear from, if it is still there, or even one from the parts store. Also, does anyone know it the stainless steel brake lines are worth the money. I saw the whole set in Victoria British for 110, I think. it was all four wheels plus the ones that go from the hard lines to the splitter, if you understand what I mean. Will it improve braking at all?

Thanks,
Chris

Maguire

iTrader: (1)

The SS brake lines will make your brakes firmer. Because the stainless steal wont stretch under pressure like the rubber ones will. rx7.com has them for a little less. about $90. But i just ordered some from mazdatrix, since i was buying some other things from them too. But racing beat has them as well.

cveklund

Do their kits include all six? I thought their kits only had the four lines.

Maguire

iTrader: (1)

there are 3 if you have rear drum brakes, or 5 if you have all disc brakes.

cveklund

Any luck on the brake balancer?

cveklund

Just checking on the brake balancer. Has anyone tried it yet?

Chris

specRX7_22

WHO DUG THIS THREAD OUT? THIS IS OOOOOLLLLDDD. LOL